1. Technical Field of the Invention
The present invention relates in general to the field of communications systems, and in particular, by way of example but not limitation, to enabling transmitter power level convergence in wireless communications systems.
2. Description of Related Art
Access to wireless networks is becoming increasingly important and popular for business, social, and recreational purposes. Users of wireless networks now rely on them for both voice and data communications. Additionally, an ever increasing number of users demand both an increasing array of services and capabilities as well as greater and greater bandwidth for activities such as Internet surfing. To remedy the congestion caused by additional subscribers and to address demands for greater bandwidth, the wireless communications industry constantly strives to improve the number of services offered by and the capacity of their wireless networks. One approach to expanding and improving the infrastructure necessary to provide additional capacity and services is the implementation of systems designed around new standards for public land mobile networks (PLMNs). These new standards tend to be based on Code Division Multiple Access (CDMA) technology, such as the Universal Mobile Telecommunications System (UMTS), the Wide-band CDMA (WCDMA) standard, etc.
In wireless systems based on CDMA technology, it is important that the base stations connected in macro-diversity with a mobile station transmit with about the same transmitter power, where transmitter power is the output power of the base station. In this context, the same transmitter power implies that the mobile station receives signals from the multiple base stations at approximately the same power level. Furthermore, it is even more important that the mobile station transmit with a power that is controlled by the base stations.
In macro-diversity connections, the base station that requires the lowest power from the mobile station controls. This implies that if one base station instructs the mobile station to increase power while another base station instructs the mobile station to decrease power, the mobile station should and will decrease transmitter power. These principles generally apply to most, if not all, CDMA-based systems.
In at least some CDMA systems, transmitter power at base stations and mobile stations is controlled by bits sent over the air interface. The bits instruct the other entity (e.g., a mobile station instructs a base station or vice versa) in a wireless communication to increase or decrease power. In a macro-diversity uplink context, the situation is relatively easy because there is only one mobile station that is receiving bit-based instructions for raising or lowering transmitter power. The mobile station simply compares the various received instructions and transmits with the lowest power as demanded by one or more base stations. In a macro-diversity downlink context, on the other hand, the situation is significantly more tricky as there are multiple base stations simultaneously transmitting, and each of the multiple base stations should coordinate their respective transmitter power outputs. There are unfortunately different predicaments that the mobile station and the multiple base stations may encounter while engaged in a macro-diversity communication that are not currently solved or handled by any existing standard or any other conventional approaches.
The deficiencies and oversights of existing approaches are overcome by the methods, systems, and arrangements of the present invention. For example, as heretofore unrecognized, it would be beneficial if base station transmitter power could be adjusted to avoid un-balanced base station transmitter power situations in macro-diversity communications. In fact, it would be beneficial if base station transmitter power could be adjusted so as to enable base station transmitter power convergence, or reception power balance at the mobile station, from the multiple base station transmissions.
Methods, systems, and arrangements in accordance with the present invention enable balanced base station transmitter output power levels with respect to a receiving mobile station in a macro-diversity communication. In macro-diversity communications, the receiving mobile station needs to control the transmitter output power level of the downlink channel, which includes transmissions from at least two transmitting base stations. However, the mobile station only sends one set of Transmission Power Control (TPC) bits in the uplink channel to all the base stations in the macro-diversity communication. Consequently, power control instructions that are appropriate for one base station may be received at and acted on by one or more of the other base stations. Additionally, because the base station requesting the lowest transmission output power level from the mobile station dominates, base stations that need a higher transmission output power level may not receive requests from the mobile station to increase their own power level.
Moreover, different channels to and from the various base stations involved in a macro-diversity communication may have differing bit error rates (BERs). One of the inherent problems with power control schemes is that the measured power corresponds to a first direction (e.g., the downlink/uplink) while the TPC bits to control the measured power are transmitted in a second direction (e.g., the uplink/downlink). The TPC bits are thus transmitted on a channel that is opposite to that of the measured channel, and each channel may be under the effects of different BERs, which further hinders the ability of a traditional power control scheme to recover from an unbalanced power level situation. In effect for traditional power control schemes, TPC bits may be wrong, may be received inappropriately, or may not be received appropriately by the various intended base stations, causing a situation where the transmission output power of one or more base stations may become unbalanced or become even more unbalanced. The present invention ameliorates this unbalanced situation by adjusting base station transmitter output power level responsive both to the power control instructions from the mobile station and to the respective current base station transmitter power output levels. Advantageously, application of the principles of the present invention enable the ultimate convergence of power output levels regardless of the extent of the initial unbalanced power level situation or situations.
In certain fixed adjustment step embodiment(s), a base station in a macro-diversity communication adjusts transmitter output power level in fixed steps. If a base station is above a reference threshold transmitter power output level, a received power control command to increase transmitter output power causes the base station to increase the transmitter output power level by an amount less than a nominal adjustment step amount, and a received power control command to decrease transmitter output power causes the base station to decrease the transmitter output power level by an amount greater than the nominal adjustment amount. If, on the other hand, a base station is below a reference threshold transmitter power output level, a received power control command to increase transmitter output power causes the base station to increase the transmitter output power level by an amount greater than a nominal adjustment step amount, and a received power control command to decrease transmitter output power causes the base station to decrease the transmitter output power level by an amount less than the nominal adjustment amount. In certain continuous adjustment step embodiment(s), the adjustment steps implemented by the base station are determined according to a continuously varying smooth function. The continuously varying smooth function provides for a gradual change in the power adjustment step as determined responsive to an increase/decrease power control command and the current transmitter output power level of the relevant base station. (It should be noted that the term xe2x80x9cfunctionxe2x80x9d, as used herein, may also refer to graphs and/or equations with two or more identical x-axis (abscissa) values.)
Implementation of certain principles in accordance with the present invention enable a balanced transmitter output power relationship of two or more base stations with respect to a mobile station in a macro-diversity communication. The balanced transmitter output power relationship is enabled, at least in part, by adjusting the transmitter output power level of a given base station of the two or more base stations by a greater amount (e.g., than a nominal amount) when a power control command orders a power adjustment of the current transmitter output power level towards a reference level and by adjusting the transmitter output power level of a given base station by a lesser amount (e.g., than the nominal amount) when a power control command orders a power adjustment of the current transmitter output power level away from the reference level.